The present invention relates to an automatic transmission and more particularly to a hydraulic control system for an automatic transmission capable of selecting six forward speed range automatic transmission and three forward speed range automatic transmission through the operation of a manual selector valve.
Generally, an automatic transmission for a motor vehicle comprises a fluid torque converter and a transmission gear having three forward range gearings and a single reverse gearing. In order to comply with the increasing demand for the economical running of motor vehicles, an automatic transmission capable of four forward speed range automatic transmission has been developed, in which an additional gear unit comprising an over-drive gearing of a high speed range and a low speed range gearing is provided for the conventional transmission gear as described hereinbefore.
The number of forward speed ranges of a transmission will be required to be increased still further in order to attain economical running of motor vehicles corresponding to versatile running conditions.
What is needed to comply with such a requirement is a compact and highly reliable hydraulic control system for a vehicle automatic transmission having multiple forward speed range gearings.